The analysis of heat transfer of automotive exhaust system is most important since their prominence in the design and also in the optimization phase of exhaust after treatment system.This paperdeals with the process which can be useful to predict the overall heat transfer coefficient for the transient flow of pipe in the after treatment system. This considers the convection of heat along gas flow, the convection between gas and wall, conduction through wall, radiation and of course convection to the ambient. Governing equations are obtained for the transient flow in a pipe for calculating gas temperature and wall temperature at distance x and time t. Analytical solution will be computed using CFD techniques for these governing equations. From the obtained analytical solution to the transient flow in pipe an excel tool will be developed which can be able to give the outlet temperature of the pipe in transient flow at length x and time t, total heat loss from pipe to the ambient, overall heat transfer coefficient for the pipe.
